The present invention relates to a semiconductor wafer grinding method and, more specifically, to a method of grinding a semiconductor wafer using a grinding machine having a chuck table for holding a semiconductor wafer and a grinding means for grinding the top surface of the semiconductor wafer held on the chuck table.
As known to people having ordinary skill in the art, in a semiconductor device production process, a substantially disk-like semiconductor wafer is divided into pellets to form semiconductor chips. To improve the heat radiation properties of the semiconductor chip, the thickness of the semiconductor chip is desirably made as small as possible. To enable the downsizing of portable telephones, smart cards, personal computers and the like in which a large number of semiconductor chips are used, the semiconductor chip is desirably formed as thin as possible. To this end, before the semiconductor wafer is divided into pellets, the rear side of the semiconductor wafer is ground to machine it to have a predetermined thickness. In the grinding machine for grinding the back surface of a semiconductor wafer, the semiconductor wafer as a workpiece is suction-held on a chuck table, and the rear side (top surface) of the semiconductor wafer whose top surface is suction-held on the chuck tablet is ground by a grinding means.
When the semiconductor wafer is ground to a thickness of 100 m or less, for example, the rigidity thereof lowers and consequently, flexure occurs all over the semiconductor wafer, thereby making it difficult to carry it and store it in a cassette. In a production method so-called xe2x80x9cpre-dicingxe2x80x9d in which, before the rear side of the semiconductor wafer is ground, dicing grooves having a predetermined depth from the surface are formed by a dicing machine and then, the rear side of the semiconductor wafer is ground to a thickness of about 50 m to divide the semiconductor wafer into chips. Though the ground semiconductor wafer is not divided into chips by the function of a protective tape affixed to the front side of the semiconductor wafer, it does not have rigidity at all as a semiconductor wafer, thereby making it extremely difficult to carry and store it in a cassette after grinding.
To make it easy to carry the ground semiconductor wafer, the semiconductor wafer is bonded to a substrate having high rigidity, this substrate having the semiconductor wafer bonded thereto is placed on the chuck table, and the semiconductor wafer is ground so that the semiconductor wafer can be carried and can be stored in a cassette easily without occurrence of flexure due to the rigidity of the substrate even after the semiconductor wafer is made thin by grinding. However, in a grinding machine in which the finishing accuracy of the semiconductor wafer is determined by the surface accuracy of the chuck table and the grinding surface accuracy of the grinding means, the interposition of the substrate between the semiconductor wafer and the chuck table causes a reduction in finishing accuracy.
It is an object of the present invention to provide a semiconductor wafer grinding method which makes it possible to carry a ground semiconductor wafer smoothly without a reduction in finishing accuracy caused by grinding.
To attain the above object, according to the present invention, there is provided a method of grinding a semiconductor wafer using a grinding machine having a chuck table for holding a semiconductor wafer and a grinding means for grinding the top surface of a semiconductor wafer held on the chuck table, comprising:
the step of placing the semiconductor wafer to be ground on the chuck table;
the step of grinding the top surface of the semiconductor wafer placed on the chuck table to a predetermined thickness by means of the grinding means;
the step of carrying out the ground semiconductor wafer from the chuck table; and
the step of holding the ground semiconductor wafer carried out from the chuck table by means of a wafer holding tray.
The wafer holding tray for holding the above semiconductor wafer is constituted by an elastic pad which has innumerable voids formed in the surface and generates sucking force when negative pressure is produced by the voids crushed by restoring force generated by elasticity and adhesion and a substrate mounting the elastic pad and having communication holes for introducing negative pressure or applied pressure force into the elastic pad; and the above tray holding step is to place the semiconductor wafer carried out from the above chuck table on the surface of the elastic pad of the above wafer holding tray and introduce negative pressure into the communication holes to suction-hold the semiconductor wafer onto the elastic pad.
The above grinding machine has a cleaning means having a spinner table for placing the ground semiconductor wafer and a tray cassette for storing the above wafer holding tray; and the above tray holding step includes the sub-step of carrying out the wafer holding tray stored in the above tray cassette and placing it on the spinner table before the ground semiconductor wafer is placed on the spinner table, the sub-step of mounting the ground semiconductor wafer on the elastic pad of the wafer holding tray placed on the spinner table, and the sub-step of introducing negative pressure into the communication holes formed in the substrate of the wafer holding tray mounted on the spinner table to suction-hold the semiconductor wafer on the elastic pad.
The above grinding machine comprises a cassette for storing a ground semiconductor wafer after cleaning; and the above semiconductor wafer grinding method of the present invention further comprises the step of storing the semiconductor wafer integratedly held on the wafer holding tray in the above cassette from the cleaning means after the semiconductor wafer is cleaned with the above cleaning means.